Diagnostic efficacy of additional step-sections in colorectal biopsies originally diagnosed as normal.

Multiple "step-sections" are prepared for many diagnostic biopsies, but tissue is usually left in the block for possible additional studies. We sought to determine the frequency with which sampling the remaining tissue with additional step-sections would reveal pathologic abnormality in a series of colorectal biopsies originally diagnosed as normal. Slides of 232 cases were reviewed and classified into 7 standard diagnostic categories. Review of the original 3 slides showed pathologic abnormality to actually be present in 9 cases (3.9%). The additional step-sections revealed pathologic abnormality in 4 (1.7%) other cases, as follows: tubular adenoma, 3 cases; lymphocytic colitis, 1 case. Neither previous nor concurrent clinical or pathological information related to colorectal disease identified the cases that were more likely to yield diagnostic abnormality in the additional step-sections. However, there was a statistically nonsignificant trend for specimens with a clinical diagnosis of "polyp" to display tubular adenoma in the deeper sections. Because examination of remaining tissue yielded new diagnostic information less frequently than the observed rate of diagnostic error, reduction in interobserver error may be a more fruitful strategy for obtaining a correct diagnosis than would complete histologic sampling.